Television tuner and method thereof

ABSTRACT

The invention provides a digital television tuner having at least two brances that receive a radio frequency signal, wherein the radio frequency signal carries M channels (M is a positive integer). A target image data is generated in real time since at least one of the branches pre-extracts the image compression data of the next channel to be switched to.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The invention relates to a television tuner, and particularly to a tunerfor digital television.

(b) Description of the Related Art

An analog television is easily influenced by terrain or landscape whichbrings about poor signal receiving and large signal amplitudefluctuation. A digital television (hereinafter referred to as “digitalTV”) that overcomes the cons of an analog television not only offershigh quality image and audio but also more programs while using the sameamount of bandwidth. In addition, the digital TV also provides functionssupporting data broadcasting such that various services andinteractivities are derived from the functions. However, drawbacks suchas slow response speed and residual image during channel switching arestill unacceptable to the general public for they are perceivable tohuman vision. Therefore, the popularity of the digital TV is yet to bepromoted.

FIG. 1 illustrates a conventional digital TV tuner 10. The digital TVtuner 10 receives a digital radio frequency signal Rf while a signal issent to a control unit CS according to the user command through a remotecontroller, a channel tuner or the like. The control unit CS generates achannel control signal C to select the signal according to the channelrequested by the user. Then, the target image data T of the requestedchannel is generated after the signal is processed through filtering,demodulating, decoding. The control unit CS can be a central processingunit, CPU. The digital TV tuner 10 comprises a control unit CS, a RFtuner 11, a signal filter 12, a DTV IF demodulator 13, and a DTV imagedecoder 14. The signal filter 12 can be a surface acoustic wave (SAW)filter. The DTV image decoder 14 can be a digital TV MPEG decoder. TheRF tuner 11 receives a digital radio frequency signal Rf and extracts asignal from the digital radio frequency signal Rf for the channelrequested by the user according to the channel control signal C. Thesignal of that channel is thereby converted into a digital intermediatefrequency signal If. The signal filter 12 receives the digitalintermediate frequency signal If and generates a filtered intermediatefrequency signal If′. Then, the DTV IF demodulator 13 of the digital TVconverts the filtered intermediate frequency signal If′ into a lowfrequency image compression data Ic. The DTV image decoder 14 thendecodes the image compression data Ic into a target image data T andtransmits the target image data T to a display device (not shown in thefigure) for viewing.

At present, the image data format of the digital TV is generally chosenfrom specifications such as MPEG2, MPEG4, H.264, . . . and so forth.Assuming that the tuner 10 of the digital television is designedaccording to the MPEG standard, then the image data format is like whatis shown in FIG. 2A. The image data includes I frames, P frames, and Bframes. The I frames are scene image data and if one I frame switches toanother I frame, the scene changes. The P frames are image data of scenetranslations while the B frames are image data regarding motions otherthan the scene. Generally, the MPEG encoded image data is transmittedwith a certain sequence during transmission and decompression. As shownin FIG. 2A, when the user switches to a channel, the DTV IF demodulator13 locks on the frequency band of that channel and converts the filteredintermediate frequency signal If′ into a MPEG encoded image compressiondata Ic. Then, the DTV image decoder 14 decodes the first I frame i1emerged from the image compression data Ic. The DTV image decoder 14then receives the first emerged P frame p1. Finally, the DTV imagedecoder 14 predicts the B frame b1 based on the I frame i1 and the Pframe p1 to process the image of that channel step by step.

When the user switches to another channel, the DTV IF demodulator 13must lock onto the bandwidth of another channel and the DTV imagedecoder 14 then decodes the first emerged I frame. As the MPEG imagedata is transmitted with a certain sequence during transmission, the DTVimage decoder 14 may or may not immediately receive the I frame of theswitched channel and may receive the P frame instead. In the case ofreceiving the I frame immediately, the user will be able to see theimage of the requested channel right away. However, if the P frame isreceived first, the user will have to wait a few more seconds until theI frame is received in order to display the entire image of therequested channel. Since it is more probable to receive a P frame firstrather than an I frame, a delay will therefore appear when the userswitches channels. As shown in FIG. 2B, when the user switches tochannel 2, channel 3, and channel 4 at time t1, t2, and t3, the I framesof these channels appear at a later time of t1, t2, and t3, and thusexperiences a serious delay of the images to be displayed when the userswitches channels.

The inconvenience of the delay phenomenon while switching betweendigital TV channels has affected the promotion of digital TV. Hence, adigital TV tuner to reduce the time required for the re-locking anddecoding and to achieve fast channel switching is yet to be provided.

BRIEF SUMMARY OF THE INVENTION

In light of the above mentioned problems, one objective of the inventionis to provide a digital television tuner that reduces the requiredwaiting time when user switches channels and to provide the fast channelswitching function.

In order to achieve the above mentioned purpose, the invention providesa digital television tuner having two branches both receiving a radiofrequency signal. The radio frequency signal carries M channels (M is apositive integer). The digital TV tuner comprises two RF tuners, twosignal filters, two DTV IF demodulators, and a DTV image decoder.

The two RF tuners, provided in the two branches respectively, receivethe same radio frequency signal. A first RF tuner extracts an Nthchannel signal (N is a positive integer and N<M) from the frequency bandof the radio frequency signal and converts the Nth channel signal into afirst intermediate frequency signal. The second RF tuner extracts an(N+1)th channel signal or an (N−1)th channel signal from the frequencyband of the radio frequency signal and converts the (N+1)th channelsignal or the (N−1)th channel signal into a second intermediatefrequency signal. When the user switches forward, the second RF tunerextracts a (N+1)th channel signal according to a channel control signal.When the user switches backward, the second RF tuner extracts a (N−1)thchannel signal according to the channel control signal.

The two signal filters are provided in the two branches mentioned above,respectively. The first filter filters the first digital intermediatedfrequency signal to generate a first filtered intermediated frequencysignal. The second filter filters the second digital intermediatedfrequency signal to generate a second filtered intermediated frequencysignal.

The two DTV IF demodulators are provided in the two branches mentionedabove, respectively. The first DTV IF demodulator receives the firstfiltered intermediate frequency signal to convert into a first imagecompression data. The second DTV IF demodulator receives the secondfiltered intermediate frequency signal to convert into a second imagecompression data.

The DTV image decoder receives and stores the first and the second imagecompression data and converts the first image compression data into afirst target image data. The DTV image decoder converts the second imagecompression data into a second target image data when the user switchesthe channel to a channel including the second image compression data.

According to the invention, a digital TV tuner (such as a tuner with 3branches) having Pn (Pn is a positive integer) branches and two methodsfor digital television tuning will be described in the following detaildescription of the invention.

According to the invention, the digital TV tuner utilizes more than 2(including 2) branches for pre-extracting the compressed image data ofthe next channel that the user may possibly switch to, when the userswitches channel forward or backward. Hence, when the user switches tothe next channel, the I frame of the corresponding channel can beaccessed immediately from the compressed image data that has beenalready stored in the DTV image decoder without waiting for such I frameextracted from the compressed image data. Therefore, real time channelswitching and fast TV channel selection can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram illustrating the digital television tuneraccording to the prior art.

FIG. 2A shows a data format diagram illustrating an image data processedby the MPEG encoding specification.

FIG. 2B shows a data flow timing sequence diagram illustrating the delayphenomenon happening while channel switching for a digital televisiontuner according to the prior art.

FIG. 3A shows a block diagram illustrating an embodiment of the digitaltelevision tuner of the invention.

FIG. 3B shows a data flow diagram illustrating the timing sequence whilechannel switching for a digital television tuner of FIG. 3A.

FIG. 3C shows a data flow diagram illustrating another timing sequencewhile channel switching for a digital television tuner of FIG. 3A.

FIG. 3D shows a data flow diagram illustrating another timing sequencewhile channel switching for a digital television tuner of FIG. 3A.

FIG. 4A shows a block diagram illustrating another embodiment of thedigital television tuner of the invention.

FIG. 4B shows a data flow diagram illustrating the timing sequence whilechannel switching for a digital television tuner of FIG. 4A.

FIG. 5 shows a block diagram illustrating another embodiment of thedigital television tuner of the invention.

FIG. 6A shows a block diagram illustrating another embodiment of thedigital television tuner of the invention.

FIG. 6B shows a block diagram illustrating another embodiment of thedigital television tuner of the invention.

FIG. 7 shows a block diagram illustrating another embodiment of thedigital television tuner of the invention.

FIGS. 8A and 8B show flow chart diagrams illustrating an embodiment ofdigital television station selection method of the invention.

FIG. 9 shows a flow chart diagram illustrating another embodiment ofdigital television station selection method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description of the invention will be given herein withreference to the drawings in which one element is represented by thesame symbol.

FIG. 3A shows a preferred embodiment of the digital TV tuner 30illustrated according to the invention. The digital TV tuner 30comprises two branches 31 and 32, both receiving radio frequency signalRf that carries M channels (M is a positive integer). The digital TVtuner 30 comprises a control unit CS, two RF tuners 311, 321, two signalfilters 312, 322, two DTV IF demodulators 313, 323, and a DTV imagedecoder 14′.

The control unit CS generates a channel control signal C′ according tothe signal transmitted from a remote controller, a tuner unit or thelike that is used for switching channels.

The RF tuners 311 and 321 are provided in the two branches,respectively. Both of the RF tuners receive the digital radio frequencysignal Rf. The first RF tuner 311 extracts an Nth channel signal (N is apositive number and N<M) from the frequency band of the digital radiofrequency signal Rf according to the channel control signal C′ andconverts the Nth channel signal into a first digital intermediatefrequency signal If1. The second RF tuner 321 extracts an (N+1)thchannel signal or an (N−1)th channel signal from the frequency band ofthe digital radio frequency signal Rf according to the channel controlsignal C′ and converts the (N+1)th channel signal or the (N−1)th channelsignal into a second digital intermediate frequency signal If2. When theuser has a tendency of switching channels forward, the second RF tuner321 records the current channel switching mode to be “forward channelswitching” through a general learning mechanism and extracts the (N+1)thchannel signal from the frequency band of the digital radio frequencysignal Rf according to the channel control signal C′. For example, asthe user switches from the 2^(nd) channel (the Nth channel) to the3^(rd) channel (the (N+1)th channel), the second RF tuner 321 startslearning and is programmed into the mode of extracting the (N+1)thchannel signal simultaneously whenever there is channel switching. Sincethe new number for N is now 3, the second RF tuner 321 not only extractsthe 3^(rd) channel signal but also pre-extracts the 4^(th) channelsignal for further processing by the device. When the user has atendency of switching channels backward, the second RF tuner 321 recordsthe current channel switching mode to be “backward channel switching”through the learning mechanism and extracts the (N−1)th channel signalfrom the frequency band of the digital radio frequency signal Rfaccording to the channel control signal C′. For example, as the userswitches from the 3^(rd) channel (the Nth channel) to the 2^(nd) channel(the (N−1)th channel), the second RF tuner 321 starts learning and isprogrammed into the mode of extracting the (N−1)th channel signalsimultaneously whenever there is channel switching. Since the new numberfor N is now 2, the second RF tuner 321 not only extracts the 2^(nd)channel signal but also pre-extracts the first channel signal forfurther processing by the device. It should be noted that in the presentembodiment the second RF tuner 321 is designed to include the learningmechanism. Obviously, in another embodiment, the learning mechanism canbe included in the control unit CS or the first RF tuner 311.

The signal filters 312 and 322 can be SAW filters, provided in the twobranches respectively. The first signal filter 312 receives the firstintermediate frequency signal If1 to perform filtering operation andthereby generate a first filtered intermediate frequency signal If1′.The second filter 322 receives the second intermediate frequency signalIf2 to perform filtering operation and thereby generate a secondfiltered intermediate frequency signal If2′.

The DTV IF demodulators 313 and 323 are also provided in the twobranches. The first DTV IF demodulator 313 receives the first filteredintermediate frequency signal If1′ and converts the filteredintermediate frequency signal If1′ into a first low-frequency imagecompression data IC1. The second DTV IF demodulator 323 receives thesecond filtered intermediate frequency signal If2′ and converts thefiltered intermediate frequency signal If2′ into a second low-frequencyimage compression data IC2.

The specification of the DTV image decoder 14′ can be selected from thegroup including the following: MPEG2, MPEG4, WMV9, VC1, DWVX and H.264(but not limited to these specifications). The DTV image decoder 14′receives the first image compression data IC1 and the second imagecompression data IC2, stores these image compression data into a memoryunit (not shown in the figure), decodes the first image compression dataIC1 into a first target image data T1, and then transmits it to adisplay device (not shown in the figure). It should be noted that theDTV image decoder 14′ only decodes the second image compression data IC2into a second target image data T2 and then transmits the second targetimage data T2 to the display device whenever the user switches to thechannel that includes the second image compression data IC2.

Referring to FIGS. 3A, 3B, and 3C, a detailed description about theoperation principle of the digital television tuner 30 of the inventionwill be given as follows. As shown in FIGS. 3B and 3C, the unit of the Xcoordinate is time. The “radio frequency tuning process” on the Y-axisrefers to the process of utilizing the RF tuners 311 and 321 and thesignal filters 312 and 322 to process the digital radio frequency signalRf. The “intermediate frequency demodulating process” on the Y-axisrefers to the process of utilizing the DTV IF demodulators 313 and 323to process the first and the second filtered intermediate frequencysignals If1′ and If2′. The “bit stream storing process” on the Y-axisrefers to the process of utilizing the DTV image decoder 14′ to storethe first and the second image compression data IC1 and IC2 (also calledbit streams IC1 and IC2). The “image decoding process” on the Y-axisrefers to the process of utilizing the DTV image decoder 14′ to decodethe image compression data of the channel currently requested by theuser.

Referring to FIG. 3B, let us assume that the user's channel switchingmode is “forward channel switching”. Thus at time t0, the first RF tuner311 and the second RF tuner 321 extract the 1st channel signal (i.e. the“Nth” channel signal) and the 2nd channel signal (i.e. the “(N+1)th”channel signal) from the frequency band of the digital radio frequencysignal Rf according to the channel control signal C′. The 1st channelsignal is hereinafter referred to as “channel 1” and the 2nd channelsignal is hereinafter referred to as “channel 2”, such as “channel N”refers to “the Nth channel”. Channel 1 and channel 2 are processed byradio frequency tuning and intermediate frequency demodulating in thebranches 31 and 32, respectively. Then, the image compression data IC1and IC2 of the channels 1 and 2 are stored by the DTV image decoder 14′.Since the user has chosen channel 1 for the meantime, the DTV imagedecoder 14′ decodes the image compression data IC1 of the channel 1 onlyand transmits the decoded target image data T1 to the display device. Itshould be noted that the DTV image decoder 14′ has already stored theimage compression data IC2 of the next channel (channel 2) that the usermay switch to.

At time t1, the user switches forward to channel 2 where N=2 and thesecond RF tuner 321 records the user's switching mode to be “forwardchannel switching”. The first RF tuner 311 and the second RF tuner 321extract channel 2 (N) and channel 3 (N+1) from the frequency band of thedigital radio frequency signal Rf, respectively. Channel 2 and channel 3are processed by radio frequency tuning and intermediate frequencydemodulating in branches 31 and 32. Since the DTV image decoder 14′ hasstored the image compression data IC2 of channel 2 before channelswitching, the stored image compression data IC2 of channel 2 can bedecoded directly and the I frame of the MPEG image data will be capturedimmediately. Therefore, the target image data T2 is generated completelyin real time and the image of channel 2, which had been requested by theuser, is displayed. The delay caused by waiting for the I frame ofchannel 2 to be displayed no longer happens. It should be noted that, atthe same time, the DTV image decoder 14′ has already stored the imagecompression data IC3 of the next channel (channel 3) that the user mayswitch to. Thereafter, at time t2, t3, and t4, the process may run inthe same manner.

Referring to FIG. 3C, by assuming that the user's channel switching modeis “backward channel switching”, then at time to, the first RF tuner 311and the second RF tuner 321 will extract channel 5 and channel 4 fromthe frequency band of the digital radio frequency signal Rf according tothe channel control signal C′. Channel 5 and channel 4 are processedwith radio frequency tuning and intermediate frequency demodulating inthe branches 31 and 32, respectively. Then, the image compression dataIC5 and IC4 of the channels 5 and 4 are stored by the DTV image decoder14′. Since the user has chosen channel 5 for the meantime, the DTV imagedecoder 14′ decodes the image compression data IC5 of channel 5 andtransmits the decoded target image data T1 to the display device. Itshould be noted that the DTV image decoder 14′ also stores the imagecompression data IC4 of the next channel (channel 4) that the user mayswitch to.

At time t1, the user switches backward to channel 4 where N=4 and thesecond RF tuner 321 records the user's channel switching mode to be“backward channel switching”. The first RF tuner 311 and the second RFtuner 321 extract channel 4 (N) and channel 3 (N−1) from the frequencyband of the digital radio frequency signal Rf, respectively. Channel 4and channel 3 are processed with radio frequency tuning and theintermediate frequency demodulating in the branches 31 and 32. Since theDTV image decoder 14′ has stored the image compression data IC4 ofchannel 4 beforehand, the stored image compression data IC4 of channel 4can be decoded directly, i.e. the I frame of the MPEG image data iscaptured immediately during channel switching. Thus, the target imagedata T2 is completely generated in real time and the image of channel 4requested by the user is displayed. The delay caused by waiting for theI frame of the MPEG image data no longer happens. It should be notedthat, at the same time, the DTV image decoder 14′ has also stored theimage compression data IC3 of the next channel (channel 3) that the usermay switch to. Thereafter, at time t2, t3, and t4, the process may runin the same manner.

According to the above mentioned method, the digital TV tuner 30 is ableto pre-extract the image compression data of the next channel that theuser may possibly switch to through the learning mechanism provided inthe second RF tuner 321 or the control unit CS during continuous channelswitching, either forward or backward (or a tendency of switching eitherforward or backward). The problem of delay in displaying images duringchannel switching thereby is resolved.

In addition, another preferred embodiment of the digital TV tuner 30 canbe as follows. Referring to FIGS. 3A and 3D, the definitions of thecoordinates of the X and Y axes in FIG. 3D are the same as those inFIGS. 3B and 3C whereas details are omitted here for brevity. First ofall, it is assumed that the user's channel switching mode is “forwardchannel switching”, then at time t0 the first RF tuner 311 and thesecond RF tuner 321 extract channel 1 and channel 2 from the frequencyband of the digital radio frequency signal Rf according to the channelcontrol signal C′, respectively. Channel 1 and channel 2 are processedwith radio frequency tuning and intermediate frequency demodulating inthe branches 31 and 32, respectively. Then, the image compression dataIC1 and IC2 of the channels 1 and 2 are stored by the DTV image decoder14′. Since the user has chosen channel 1 for the meantime, the DTV imagedecoder 14′ decodes the image compression data IC1 of the channel 1 togenerate a target image data T1 and transmits the target image data T1to the display device. It should be noted that the DTV image decoder 14′has already stored the image compression data IC2 of the next channel(channel 2) that the user may switch to.

At time t1, the user switches forward to view channel 2 where N=2 andthe control unit CS records the user's channel switching mode to be“forward channel switching” and generates the channel control signal C′to assign the first RF tuner 311 to extract the (N+1) channel and thesecond RF tuner 321 to extract the (N) channel. Thus, the first RF tuner311 and the second RF tuner 321 extract channel 3 (N+1) and channel 2(N) from the frequency band of the digital radio frequency signal Rf,respectively, and channel 3 and channel 2 are processed with radiofrequency tuning and intermediate frequency demodulating in the branches31 and 32, respectively. Since the DTV image decoder 14′ has stored theimage compression data IC2 of channel 2 before channel switching, thestored image compression data IC2 of channel 2 can be decoded directlyand the I frame of the MPEG image data will be captured immediately.Therefore, the target image data T2 is generated completely in real timeand the image of channel 2, which had been requested by the user, isdisplayed. The delay caused by waiting for the I frame of channel 2 tobe displayed no longer happens. It should be noted that, at the sametime, the DTV image decoder 14′ has already stored the image compressiondata IC3 of the next channel (channel 3) that the user may switch to.Thereafter, at time t2, t3, and t4, the process may run in the samemanner. On the other hand, the process regarding “backward channelswitching” should work in a similar manner is omitted here for brevity.The difference between the processing in FIG. 3D and FIG. 3B is that theprocessing in FIG. 3D does not require the RF tuner to change thechannel to be extracted each time the channel is switched, and is doneby different implementations of the design.

FIG. 4A illustrates another embodiment of the digital TV tuner 40. Thedigital TV tuner device 40 is provided with three branches 41, 42, and43. The digital TV tuner 40 comprises a control unit CS, three RF tuners411, 421, 431, three signal filters 412, 422, 432, three DTV IFdemodulator 413, 423, 433, and a DTV image decoder 14′. The structure ofthe digital TV tuner 40 is almost the same as that of the digital TVtuner 30. The difference is that the digital TV tuner 40 has oneadditional branch 43 to increase the number of pre-extracted channels sothat the channel N that the user is currently viewing, the next channel(N+1) for the case of forward channel switching, and the next channel(N−1) for the case of backward channel switching can be extractedsimultaneously. During the operation of the digital TV tuner 40, all RFtuners receive the digital radio frequency signal Rf. The first RF tuner411 extracts an Nth channel signal (N is a positive number and N<M) fromthe frequency band of the digital radio frequency signal Rf according tothe channel control signal C′ generated when the user switches channelsand converts the Nth channel signal into a first digital intermediatefrequency signal If1. The second RF tuner 421 extracts an (N+1)thchannel signal from the frequency band of the digital radio frequencysignal Rf according to the channel control signal C′ and converts the(N+1)th channel signal into a second digital intermediate frequencysignal If2. The third RF tuner 431 extracts an (N−1)th channel signalfrom the frequency band of the digital radio frequency signal Rfaccording to the channel control signal C′ and converts the (N−1)thchannel signal into a third digital intermediate frequency signal If3.The digital intermediate frequency signals If1, If2 and If3 aretransmitted to the signal filters 412, 422, and 423 and the DTV IFdemodulators 413, 423, and 433 to be processed with the conversion anddemodulation processes so as to generate the first, the second, and thethird image compression data IC1, IC2, and IC3.

Referring to FIGS. 4A, 4B, and 4C, a detailed description about theoperation principle of the digital TV tuner 40 of the invention will begiven as follows. As shown in FIG. 4B, the definitions of thecoordinates of the X, Y axes are the same as that in FIGS. 3B, 3C, and3D. First of all, at time t0, the first, the second, and the third RFtuners 411, 421, and 431 extract the channel 1 (N), channel 2 (N+1),channel 0 (N−1) from the frequency band of the digital radio frequencysignal Rf according to the channel control signal C′, respectively. Thechannels 1, 2, and 0 are processed with radio frequency tuning andintermediate frequency demodulating in the branches 41, 42, and 43,respectively. Then, the image compression data IC1, IC2, and IC0 of thechannels 1, 2, and 0 are stored by the DTV image decoder 14′. Since theuser chooses to view the channel 1 for the meantime, the DTV imagedecoder 14′ decodes the image compression data IC1 of the channel 1 andtransmits the IC1 to the display device. It should be noted that the DTVimage decoder 14′ also stores the image compression data IC2 and IC0 ofthe next channels (forward channel 2 and backward channel 0) that theuser may switch to.

At time t1, the user switches forward to view channel 2 where N=2 andthe first, the second, and the third RF tuners 411, 421, and 431 extractchannels 2(N), 3(N+1), and 1(N−1) from the frequency band of the digitalradio frequency signal Rf, respectively. Channels 2, 3, and 1 areprocessed with the radio frequency tuning and intermediate frequencydemodulating in the branches 41, 42, and 43, respectively. Since the DTVimage decoder 14′ has stored the image compression data IC2 of channel 2beforehand, the stored image compression data IC2 of channel 2 can bedecoded directly, i.e. the I frame of the MPEG image data is capturedimmediately during channel switching. Therefore, the target image dataT2 is completely generated in real time and the image of channel 2requested by the user is displayed. The delay caused by waiting for theI frame of the MPEG image data no longer happens. It should be notedthat, at the same time, the DTV image decoder 14′ has also stored theimage compression data IC3 and IC1 of the next forward channel 3 andbackward channel 1 that the user may switch to, and the imagecompression data IC0 of channel 0 that is originally stored may bedeleted.

Then, at time t2, the user switches forward to channel 3, the proceduresare the same as above. Thus, the DTV image decoder 14′ decodes the imagecompression data of channel 3 and pre-stores the image compression dataIC4 and IC2 of channels 4 and 2.

At time t3, the user starts to switch backward to channel 2 where N=2and the first, the second, and the third RF tuners 411, 421, 431 therebyextract the channels 2(N), 3(N+1), and 1(N−1) from the frequency band ofthe digital radio frequency signal Rf, respectively. The channels 2, 3,and 1 are processed with radio frequency tuning and intermediatefrequency demodulating in the branches 41, 42, and 43, respectively.Since the DTV image decoder 14′ has stored the image compression dataIC2 of channel 2 before channel switching, the stored image compressiondata IC2 of channel 2 can be decoded directly and the I frame of theMPEG image data will be captured immediately. Therefore the target imagedata T2 is generated completely in real time and the image of channel 2,which had been requested by the user, is displayed. The delay caused bywaiting for the I frame of channel 2 no longer happens.

It should be noted that, at the same time, the DTV image decoder 14′ hasalready stored the image compression data IC3 and IC1 of the nextforward channel 3 and backward channel 1 that the user may switch to andthe image compression data IC0 of the channel 0 originally stored may bedeleted. Thereafter, at time t4˜t7, the processes may run in the samemanner.

According to the above mentioned method, the digital TV tuner 40 is ableto pre-extract the image compression data of the next forward andbackward channel that the user may possibly switch to through thelearning mechanism provided in the second and the third RF tuners 421and 431 or the control unit CS during continuous channel switching,either forward or backward (or a tendency of switching either forward orbackward). The problem of delay in image displaying as seen in theconventional TV tuner 10 during channel switching is thereby resolved.

It is apparent that the operation of the digital TV tuner 40 can alsofollow the operating mode as illustrated in FIG. 3D and its detail isnot repeated here for brevity. Moreover, the more branches inutilization, the shorter the time required for channel switching. Forinstance, assume that there are Pn branches (Pn is a positive number andPn<=M), then the required waiting time for channel switching is reducedto 1/Pn th of the original required time. As illustrated in FIG. 5, thedigital TV tuner 50 includes Pn branches 51˜5 Pn and the waiting timefor channel switching of the digital TV tuner 50 becomes 1/Pn th of thatof the conventional TV tuner 10.

The concept of the digital TV tuner of the invention can be implementedin a number of different approaches. As illustrated in FIG. 6A, the PnDTV IF demodulators can be combined together and implemented by onesingle DTV IF demodulator 13′ with a bandwidth of Pn times. On the otherhand, as shown in FIG. 6B, the DTV IF demodulator 13′ and the imagedecoder 14′ can be combined into one single intermediate frequencydemodulating and image decoding device (IFDE). This approach not onlyincreases synchronization of the image data, but also reduces theconversion time of compressing and decoding. Therefore, optimum digitaltelevision channel selection is achieved. Furthermore, as shown in FIG.7, the digital TV tuner 70 of the invention can also use a filter 72with a bandwidth of Pn times and a DTV IF demodulator 73 also with abandwidth of Pn times to replace the original Pn signal filters and DTVIF demodulators, such that die area or cost is reduced.

FIGS. 8A and 8B illustrate the flow chart diagrams of a method regardinga tuner in utilization. The method includes the following steps:

Step S802: starting;

Step S804: receiving a digital radio frequency signal carrying Mchannels (M is a positive number);

Step S806: extracting the Nth channel signal from the frequency band ofthe digital radio frequency signal according to the Nth channel (N is apositive number, N<M) chosen by the user, converting the Nth channelsignal into a first image compression signal, decoding the first imagecompression signal, and generating a first target image data;

Step S808: determining if the user channel switching mode is“continuously switching channels forward” (a tendency of switchingchannels forward), and thereby jumping to step S810 if yes and to stepS816 if no;

Step S810: pre-extracting an (N+1)th channel signal from the frequencyband of the digital radio frequency signal and converting the (N+1)thchannel signal into a second image compression data;

Step S812: determining if the next channel switched by the user is the(N+1)th channel and thereby jumping to step S814 if yes and to step S824if no;

Step S814: decoding the second image compression data to generate asecond target image data and jumping to step S824;

Step S816: determining if the user channel switching mode is“continuously switching channels backward” (a tendency of switchingchannels backward) and thereby jumping to step S818 if yes and to stepS824 if no;

Step S818: pre-extracting an (N−1)th channel signal from the digitalradio frequency signal and converting the (N−1)th channel signal into athird image compression data;

Step S820: determining if the next channel switched by the user is the(N−1)th channel and thereby jumping to step S822 if yes and to step S824if no;

Step S822: decoding the third image compression data to generate a thirdtarget image data; and

Step S824: End.

It should be noted that the specification of the above mentioned first,second, and third image compression data may be selected from thefollowing, which includes: MPEG2, MPEG4, WMV9. VC1, DIVX and H.264. Thefirst, the second, and the third target image data are transmitted to adisplay device for viewing.

FIG. 9 illustrates the flow chart diagram of another method of theinvention. The method comprises the following steps:

Step S902: starting;

Step S904: receiving a digital radio frequency signal carrying Mchannels (M is a positive number);

Step S906: extracting the Nth channel signal from the frequency band ofthe digital radio frequency signal according to the Nth channel (N is apositive number, N<M) chosen by the user, converting the Nth channelsignal into a first image compression signal, and decoding the firstimage compression signal to generate a first target image data;

Step S908: pre-extracting an (N+1)th and an (N−1)th channel signal fromthe frequency band of the digital radio frequency signal and convertingthe (N+1)th and the (N−1)th channel signals into a second and a thirdimage compression data;

Step S910: determining if the next channel chosen by the user is the(N+1)th channel and thereby jumping to step S912 if yes and to step S914if no;

Step S912: decoding the second image compression data to generate asecond target image data, deleting the third image compression data, andjumping to step S824.

Step S914: determining if the next channel chosen by the user is the(N−1)th channel and thereby jumping to step S916 if yes and to step S918if no;

Step S916: decoding the third image compression data to generate a thirdtarget image data and deleting the second image compression data; and

Step S918: End.

It should be noted that the specification of the above mentioned first,second, and third image compression data may be selected from thefollowing, which includes: MPEG2, MPEG4, WMV9. VC1, DIVX and H.264. Thefirst, the second, and the third target image data are transmitted to adisplay device for viewing.

The process of decoding and outputting image compression data should bemodified according to the actual requirements (such as for overcominghardware limitation, boosting effects, . . . , and so forth), regardlessof the device or the method in the embodiments mentioned above. Forinstance, the image compression data stored in the memory unit can beaccessed directly, in order to acquire the I frame and the P frame. TheI frame and P frame or the P frame and B frame suitably acquired fromthe P frame are thus utilized. Otherwise, the I frame or P frame may bedisplayed directly.

Although the present invention has been fully described by the aboveexamples with reference to the accompanying drawings, it should be notedthat various changes and modifications may be made by those skilled inthe art without departing from the scope of the present invention.

1. A tuner, having Pn branches (Pn is a positive integer), all receivinga radio frequency signal that carries M channels (M is a positiveinteger and M≧Pn), comprising: Pn radio frequency tuners, provided inthe Pn branches for receiving the radio frequency signal, respectively,a first radio frequency tuner extracting an Nth channel signal (N is apositive integer and N<M) from the frequency band of the radio frequencysignal and converting the Nth channel signal into a first intermediatefrequency signal while a second radio frequency tuner extracting an(N+1)th channel signal or an (N−1)th channel signal from the frequencyband of the radio frequency signal and converting the (N+1)th channelsignal or the (N−1)th channel signal into a second intermediatefrequency signal, wherein the Pn radio frequency tuners convert Pnchannel signals into Pn intermediate frequency signals; and anintermediate frequency demodulating and image decoding device forconverting the first intermediate frequency signal and the secondintermediate signal into a first image compression data and a secondimage compression data and decoding the first image compression datainto a target image data, wherein the second image compression data isdecoded into the target image data when a user switches the channel to achannel comprising the second image compression data.
 2. The tuner asclaimed in claim 1, wherein the second radio frequency tuner extractsthe (N+1)th channel signal when the user switches channels forward andthe second radio frequency tuner extracts the (N−1)th channel signalwhen the user switches channels backward.
 3. The tuner as claimed inclaim 1, wherein a third radio frequency tuner extracts the (N−1)thchannel signal while the second radio frequency tuner extracts the(N+1)th channel signal and the third radio frequency tuner extracts the(N+1)th channel signal while the second radio frequency tuner extractsthe (N−1)th channel signal.
 4. The tuner as claimed in claim 3, whereina third image compression data corresponding to the (N−1)th channel isdeleted when the user switches from the Nth channel to the (N+1)thchannel or the third image compression data corresponding to the (N+1)thchannel is deleted when the user switches from the Nth channel to the(N−1)th channel.
 5. The tuner as claimed in claim I, further comprising:Pn signal filters, provided in the Pn branches, respectively, a firstsignal filter filtering the first intermediate frequency signal, asecond signal filter filtering the second intermediate frequency signal,wherein the Pn signal filters filter Pn intermediate frequency signals.6. The tuner as claimed in claim 1, further comprising: a signal filterwith a bandwidth of Pn times, for filtering a number of Pn intermediatefrequency signals.
 7. The tuner as claimed in claim 1, wherein theintermediate frequency demodulating and image decoding device comprisesan intermediate frequency demodulator for converting the first and thesecond intermediate frequency signals into the first and the secondimage compression data, wherein the intermediate frequency demodulatorconverts Pn intermediate frequency signals into Pn image compressiondata.
 8. The tuner as claimed in claim 7, wherein the intermediatefrequency demodulator comprises an intermediate frequency decoder with abandwidth of Pn times.
 9. The tuner as claimed in claim 1, wherein theintermediate frequency demodulating and image decoding device comprisesPn intermediate frequency demodulators for converting the first, thesecond, . . . and the (Pn)th intermediate frequency signals into thefirst, the second, . . . and the (Pn)th image compression data,respectively.
 10. The tuner as claimed in claim 1, wherein theintermediate frequency demodulating and image decoding device comprisesan image decoder for decoding the first, the second, . . . or the (Pn)thimage compression data into the target image data.
 11. The tuner asclaimed in claim 5, wherein each of the Pn signal filters comprises asurface acoustic wave filter.
 12. The tuner as claimed in claim 10,wherein the specification of the image decoder is selected from thegroup consisting of the following: MPEG2, MPEG4, WMV9. VC1, DIVX andH.264.
 13. The tuner as claimed in claim 10, wherein the first, thesecond, . . . or the (Pn)th image compression data is decoded into thetarget image data to display the I frame and the P frame or the P frameand the suitable B frame derived from the P frame or displaying the Iframe or the P frame directly.
 14. The tuner as claimed in claim 10,wherein the image decoder stores the first, the second, . . . and the(Pn)th image compression data into a memory unit.
 15. A method for atuner in utilization, comprising: receiving a radio frequency signalthat carries M channels (M is a positive integer); extracting an Nthchannel signal from the frequency band of the radio frequency signal inaccordance with the Nth channel (N is a positive integer and N<M)selected by a user; converting the Nth channel signal into a first imagecompression data; decoding the first image compression data into atarget image data; pre-extracting an (N+1)th channel signal or an(N−1)th channel signal from the frequency band of the radio frequencysignal; converting the (N+1)th channel signal or the (N−1)th channelsignal into a second image compression data; and decoding the secondimage compression data into the target image data when the user switchesto the channel corresponding to the second image compression data. 16.The method for the tuner in utilization as claimed in claim 15, furthercomprising: pre-extracting the (N+1)th channel signal from the frequencyband of the radio frequency signal when the user has a tendency ofswitching channels forward and pre-extracting the (N−1)th channel signalfrom the frequency band of the radio frequency signal when the user hasa tendency of switching channels backward.
 17. The method for the tunerin utilization as claimed in claim 15, wherein the (N−1)th channelsignal is also extracted while extracting the (N+1)th channel signal,and vise versa.
 18. The method for the tuner in utilization as claimedin claim 17, wherein a third image compression data corresponding to the(N−1)th channel is deleted when the user switches from the Nth channelto the (N+1)th channel or the third image compression data correspondingto the (N+1)th channel is deleted when the user switches from the Nthchannel to the (N−1)th channel.
 19. The method for the tuner inutilization as claimed in claim 18, wherein the second or the thirdcompression data is decoded into the target image data to display the Iframe and the P frame or the P frame and the suitable B frame derivedfrom the P frame or displaying the I frame or the P frame directly. 20.The method for tuner in utilization as claimed in claim 17, wherein thetarget image data is outputted to a display device for viewing.